/**
 * @author rain-falling-cold-s
 **/
public class Test2 {
    public static void main(String[] args) {
        //1/1-1/2+1/3-1/4+1/5 …… + 1/99 - 1/100
        double d;
        double sum = 0;
        for (d = 1.0; d <= 100.0; d++) {
            if (d % 2 == 0.0) {
                sum = sum - 1 / d;
            } else {
                sum = sum + 1 / d;
            }
        }
        System.out.println(sum);
    }
}
